When I was teaching my policy was to reconsider anything a student felt was a mistake in grading, as long as it was accompanied by a written memo explaining precisely what the mistake was. I found this to be a good way to ensure I was getting legitimate regrade requests, since students would only put in the effort to write the memo if they really felt something was wrong.
That the teacher has made one mistake implies the teacher may have made more than one mistake, and there's some probability that those errors are in your favor. And if its really correctness you're worried about, rather than just going for a better grade, then you should be okay with a full on review. But you should be confident that there are errors, rather than just winging it for the occasional payoff.
WTF does that even mean?
Look, I'm a student. I'm supposed to make mistakes. It's natural for me to be wrong. I should be wrong many times now so that I can learn and not make those mistakes in the future.
But you're a teacher. You are supposed to correct mistakes. You are supposed not to make mistakes, or at the very least to be honest about those mistakes. You're not supposed to try to intimidate me so that I stop questioning you; you're supposed to encourage critical thinking and healthy scepticism.
In short: if a teacher hears that he made a mistake when grading it's his duty to check it again, carefully; and if it happens to be true he should be honest about it and admit it instead of threatening that he'll lower the grade even further. What your teacher said could be read as: "Ok, so I may have fucked up, but that doesn't matter, because I'm so much smarter than you and I can fuck you up in any way I'd like; do you want me to show you?" Your teacher probably didn't mean it that way, but I met a fair share of teachers who did; it would be best to stay away from such ambiguous phrasings altogether.